The present disclosure relates to energetic compositions, more specifically to bonding agents in energetic compositions.
Energetic compositions include solid particles dispersed in a rubbery matrix, called a binder. A compound that provides oxidizing chemical species to the combustion process and/or liberates energy upon decomposition is a common type of particle used in energetic compositions. The structural properties of the compositions are influenced by the strength of the bond between the binder and the surfaces of the solid particles. Since the oxidizers can make up a majority of the particulate matter, the bond between the binder and the oxidizer particle surfaces has a significant effect on composition's structural properties.
A number of effective bonding agents exist for composite energetic compositions in which ammonium perchlorate (AP) is the principal oxidizer. AP is a common oxidizer in such compositions and chemically reacts with many types of compounds. However, effective bonding agents for propellants in which nitrogen-containing oxidizers, which are less reactive, are the principal solid oxidizer are unknown. Two common nitrogen-containing oxidizers used in energetic compositions are cyclotetramethylenetetranitramine (HMX) and cyclotrimethylenetrinitramine (RDX).
Generally, an effective bonding agent will coat the oxidizer surface, chemically react to form an encapsulating film around the particles, and bond to the binder either chemically or adhesively. If the bonding agent film then has sufficient affinity for the oxidizer surface it will prevent binder/oxidizer separation under stress. The bonding agent may be coated onto the oxidizer particles either before incorporation of the oxidizer into the composition mix or, in some cases, during the composition mixing operation.
The structural properties of energetic compositions derive from a complex interaction of binder properties with the solid oxidizer particles. Further, the composition properties are strongly influenced by particle size and volumetric loading, as well as by the binder/solids bond strength. When the elastomeric binder is strong relative to the binder/solids bond strength, a composition under sufficient tension will undergo separation of the binder from the solids. The separation is sometimes referred to as de-wetting or blanching and is followed by large extensions of the binder prior to rupture. Structurally, such a composition is characterized by high extensibility and low tensile strength. However, when the binder/solids bond strength is increased, as by a bonding agent, de-wetting is prevented or forestalled, resulting in less extensibility and higher tensile strength.